~the sample proportion is used to estimate the population proportion in a given study. It comes from the sample we take. Since many problems deal with estimating the minimum sample size for the true population proportion at a given margin of error, we do not know the sample proportion in advance. So, we need to estimate it either by a prior study or some other means. In cases where we have no idea of what to use for the sample proportion, .5 is used. We then use p cap (sample proportion) for that estimate, get q cap (1- p cap), then use the formula for E (for proportions, see below), break up the square root over the fraction, switch the square root of n with E, the calculate the right side, then square, then round up for our required minimum sample size n.